The avalanche occurred at the Rio Tinto-Kennecott Utah Copper’s open-pit Bingham Canyon Mine, 20 miles southwest of downtown Salt Lake City, where each of the rock avalanches lasted about 90 seconds.

Researchers said that mining officials had monitored movements in the 107-year-old copper mine and identified increasing instability in the months before the slide. The instability led officials to close and remove the visitor's center as a safety precaution.

Mining officials told GSA Today that the mine produces 25 percent of the copper used in the United States. At 3,182 feet deep, the mine is the likely the world's largest man-made excavation site.

"This is really a geotechnical monitoring success story," Kris Pankow, associate director of the University of Utah Seismograph Stations and a research associate professor of geology and geophysics, said. "No one was killed, and yet now we have this rich dataset to learn more about landslides."

Pankow told GSA Today that April's avalanche was felt throughout the Utah seismic network and as far away as 250 miles south, on the Utah-Arizona border.

The Associated Press noted that Mount St. Helens' eruption in 1980 in Washington created an avalanche 57 times larger than Kennecott's. A landslide about 8,000 years ago in southern Utah's Zion Canyon was five times larger.